Fig 1: Transmission electron micrographs of fetal (gestational week 12) human neocortex showing the localization of serotonin receptor 2a (HTR2A) in NPCs by immunogold labeling.Fetal human neocortical tissue was fixed and subjected to ultrathin cryosectioning (70 nm) following a previously described protocol [35]. Sections were immunogold-labeled using rabbit-anti-HTR2a antibody (1:200, Abcam, ab140524, RRID: AB_2858218) and Protein-A–10 nm gold. Immunogold labeling of HTR2A was observed in three independent fetal human neocortical tissues. (A) Overview of the ventricular area of the VZ of fetal human neocortex. (B) Higher magnification of the boxed region in A. Note the pericentriolar immunogold labeling. (C,D) Representative images of the ventricular area of the VZ showing an unlabeled basal body (C) and HTR2A-labeled cytoplasmic vesicles (C,D). (E) Representative image of densely packed nuclei in the SVZ. (F) Higher magnification of the boxed region in E. Note the immunogold labeling for HTR2A next to the plasma membrane. Scale bars 500 nm (A,E), 100 nm (B–D,F). Arrows, gold particles; v, ventricle; asterisks, adherens junctions; c, centriole; m, mitochondrion; n, nucleus.